Whyte — 15 — Research in Vernalization 



tion, but the interval between emergence of the leaf and its death was short- 

 ened. The factor most closely connected with yield was leaf area of a 

 plant, and it was this which was markedly affected by vernalization. The 

 successive emergence of leaves was more rapid with than without vernaliza- 

 tion, and each leaf reached its maximal size sooner. A growing leaf uses 

 much of the products of metabolism for its growth ; vernalization has the 

 advantage of hastening the growth of leaves and ensuring its early comple- 

 tion, after which the products are released for the benefit of the embryonic 

 ear. It was noticed that the content of nitrogenous substances in the lowest 

 leaves was diminished after the leaves had ceased to increase in size. 



The synthetic activity of the leaves reached the maximum sooner in 

 vernalized than unvernalized plants, and, after remaining stationary for a 

 while, gradually decreased. The accumulation of dry-matter was likewise 

 more abundant in vernalized plants. Consequently there was more ma- 

 terial available for translocation to the developing ear, thus accounting for 

 the well-being of vernalized plants which is to be especially observed during 

 a dry season. 



The yield of late-maturing wheat in Konovalov's experiments was in- 

 creased by vernalization because, although tillers were reduced in number, 

 their ears bore better and more numerous spikelets, as well as more numer- 

 ous and heavier grain. In the early-maturing varieties the good develop- 

 ment of the ears could not compensate for the reduced number of tillers, and 

 vernalization did not therefore increase the yield. 



A similar result is reported by Buzovir ( 1936) , who made experiments 

 over two seasons with varieties of winter and spring wheat and a variety of 

 millet ; at the beginning of vegetative growth in winter wheat and through- 

 out the vegetative period in the other plants, the rate of elaboration and ac- 

 cumulation of dry matter was greater in vernalized plants. The accumula- 

 tion of carbohydrates was also greater in vernalized plants, particularly dur- 

 ing the period from jointing and stem elongation to milk ripeness. 



In experiments made by Zaicev.^ (1939) with spring and winter wheats 

 sown with vernalized and unvernalized seeds, it was found that the chloro- 

 phyll content increased as the plants advanced towards sexual maturity, 

 reaching a maximum of over 6 mg. of crystalline chlorophyll per grm. of 

 leaf weight in both varieties, by the time of heading or thereabouts and 

 falling rapidly thereafter. In rapidity of development, the spring wheat 

 was somewhat ahead of the vernalized winter wheat. No such regularity 

 was noted in unvernalized winter wheat plants that remained at the tillering 

 phase, the chlorophyll content varying from the beginning of tillering be- 

 tween 3 and 4 mg. of crystalline chlorophyll per grm. of leaf weight, the 

 highest figures being obtained in the leaves nearest to the spikes. Advance 

 in development is considered to be the chief factor causing this conspicuous 

 variation. 



An important aspect of Soviet research is the work of Kostjucenko 

 and Zarubailo on the vernalization of grain during the period preceding 

 dormancy while the grain is ripening on the mother plant. This is a ques- 

 tion which has very considerable practical implications, and affects all mat- 

 ters connected with plant introduction and the cultivation of plants in an 

 environment differing widely from that in which the seeds were produced. 



